US2348890A - Boiler feed water control mechanism - Google Patents

Description

INVENTOR;

HENRY C.EARLEJ& M was Le 01L ATTORNEY.

H C EARLE JR BOILER FEED WATER CONTROL MECHANISM Filed Dec. 16, 1940 May 16, 1944.

Patented May 16, 1944 BOILER FEED WATER CONTROL NIECHANISM Henry C. Earle, Jr., Philadelphia, Pa., assignor to Mason-Neilan Regulator 00., Boston, Mass, a voluntary trust of Massachusetts Application December 16, 1940, Serial No.370,367

. 8 Claims.

This invention relates to feed water control mechanism which is adapted to be used in connection with steam generators to maintain the water level within predetermined limits under varying conditions of operation.

The device herein disclosed may be applied to generators subject to relatively wide variations in vapor pressure, caused by drastic load changes, to maintain the desired water level, or may be applied togenerators in combination with automatic means for maintaining a reasonably uniform vapor pressure, subject to minor variations caused by sudden load changes, to provide a highly stabilized system of generator control. While this invention relates to means for controlling the water level in almost any type of steam boiler, it is particularly adapted to be used in connection with steam generators having a high steaming rate in relation to water capacity wherein the water level must be maintained within close limits.

As is well known to those skilled in the art, many modern boilers approach flash type units, they operate at high pressures and ratings and their combustion rates change almost instantly with rapidly fluctuating loads. Mainly because of the decreased liberating surface per developed horsepower, their water levels tend to be very sensitive and this condition is accentuated because of so-called "shrinking" and swelling of boiler water which occurs under sudden load changes. In the process of vapor generation,

- a portion of the boiler water is in the form of bubbles and when a sudden decrease in load occurs, a temporary increase in steam pressure results with a consequent shrinkage of water level, whereas a sudden increase in load creates a temporary drop in boiler pressure and a resulting swell in water level. The extent to which the boiler water shrinks or swells on a given chang in pressure is dependent on the percentage of boiler water in the form of bubbles and this, in turn, depends on the relation of the water capacity to the steaming rate. Where the steaming rate is high in relation to the water capacity, a considerable swelling and shrinking of water occurs, which complicates the problem of water level control, especially as in many boilers the safe limits of permitted level variation are within a narrow range.

While the false water level, occasioned as hereinabove described, may be of a temporary nature, it is of suflicient duration to interfere seriously with the operation of control devices responsive to variations in water level. For example, on a sudden increase in load the resulting drop in pressure and rise in water level causes the level controller, whether it be of the float operated, thermostatic, or manometer type, to reduce the supply of feed water by an amount depending on the rise in level and the throttling range of the controller. In fact, the supply of boiler water may be shut oil entirely until the false level recedes substantially to the true level. Thus, when the so-called swelling or water is over, the level rapidly drops below the set point by an amount depending on the quantity of water used during the period of swell which is in excess of the amount or water supplied during that period and which may be sufllcient to exceed the safe limits of level change. Such a condition creates a cycle in boiler operation which interferes with the efllciency and stability of the boiler and places an unnecessary strain on the feed supply mechanism, especially when a number of boilers operate on one feed water system.

While various means have been employed in an attempt to overcome this condition, all such means, so far as known to me, have been in the form of complicated and expensive systems of control which require a considerable addition to the cost of installation and upkeep.

It is an object 01' this invention to provide a compact control device of standard type which may be readily adapted to respond to small increments of level change and to vary the water feed supply accordingly.

hereinabove referred to and thereafter to return the level control setting to normal as the false water level disappears.

It is another object of this invention to provide a sensitive level responsive unit having an automatic control point reset which may be combined in one standard instrument assembly and which may be applied to a boiler, or to each unit of a battery of boilers, without the use of connections other than those required for a level response unit.

It is still another object of this invention to provide a level controller having a wide range of adjustment and adaptability, whereby it is suitable for level control purposes in connection with any type of steam generator whether or not the generator is subject to substantial changes in vapor pressure and load.

It is still another object of this invention to provide means which may operate in conjunction with automatic pressure control mechanism capable of maintaining a substantially uniform boiler pressure, subject to temporary pressure changes due to sudden changes in load, and which functions together with said pressure control means to maintain the-boiler water level within close limits thereby providing a system of boiler operation having a high degree of efliciency and stability.

Other and more specific objects and advantages of this invention will appear from the following description when taken in connection with the accompanying drawing. It will be under-' stood, however, that the drawing and description are b way of illustration only and are not intended to limit the invention except in so far as it is limited in the claims.

In the drawing Fig. 1 is a view partly in diagram of a steam boiler having an automatic steam pressure control mechanism, a feed water control valve and a water level controller embodying my invention.

Fig. 2 is a section taken substantially on the line 2--2 of Fig. 1.

Fig. 3 is a section taken substantially on the line 3-3 of Fig. 1.

Having reference to Fig. 1 of the drawing, at H! is indicated a steam boiler which may be of any conventional design and is herein shown as having tubes II, a battle 82, a steam drum l3 and a blow-down chamber Hi, the system being filled with water to the level indicated at I 5 by means of a water feed line I6 supplied from a source not shown and governed by a control valve H.

The control valve I! may be adapted to be operated by fluid under pressure, such as air, and for this purpose may have a diaphragm chamber it, one wall of which is defined by a flexible diaphragm ii! in operative connection with a stem and valve member 2|, the parts being arranged so that an increase of fluid pressure on the diaphragm l9 tends to close the valve against the action of a suitable spring 22.

The boiler It) may be fired in any convenient manner, as by fuel oil burners 25, of any well known construction, which may be supplied with fuel through a pipe 26 and header 21 from a pump or other source not shown. A suitable control valve 28, similar in construction to valve i1, may be connected to the header 2! by means of a pipe 23 and the fuel pressure on burners 25 may be governed by controlling the discharge of excess fuel to a return line 36 to the pump suction, or other source of supply. The valve 28 may be operated by fluid pressure supplied to its diaphragm chamber 3| through a line 32 which is governed by a pressure controller 33 of any well-known construction. The controller 33 may be furnished with operating fluid under pressure from a source not shown by means of a supply line 34 and may be responsive to variations in boiler steam pressure by means of a, pipe 35 connected with a steam header 36 which is in turn connected with the boiler steam drum is through a steam riser 31. The controller 33 and valve 28 are so arranged that on an increase of boiler steam pressure, the pressure of the operating fluid in diaphragm chamber 3! is reduced and the valve 28 is opened to lower the pressure on burners 25 and to cut .down the input of heat to the boiler accordingly. On a decrease in boiler pressure, the opposite occurs; It will be under stood that an air damper 38 and any other wellknown apparatus may be used to assist in the control of boiler pressure.

Means responsive to variations in water level may be in the form of an instrument of the mercury manometer type. herein shown partly in diagram for purposes of clarity. It comprises the usual mercury pots 46 and 48, interconnected by a pipe 41 and filled with mercury 43 to the levels indicated at 4'6 and 60. A pipe 6| serves to provide means of fluid communication between pct 45 and the steam drum l3 at point below the water level I 5. The pot 66 may be connected to the vapor space in drum II by means of pipes 62 and 63, a condensate chamber 64 being employed to provide a definite head of water above the mercury in pct 46. At 65 in pct 46 is a float which is pivotally connected to an arm 61, which is, in turn, rigidly attached to a shaft 58. A pressure tight bearing 69, of well-known construction, which extends through the side oi the pct 46, serves as a support and guide for the shaft in which the shaft is freely rotatable and by which leakage is prevented. It will be understood from the above description of parts that when an increase in water level occurs in the drum l3 mercury flows from the pct 45 through pipe 41 to the pot 46, thereby increasing the level of mercury in the latter; and raising the float to rotate shaft 58 in a counter-clockwise direction, and that on a decrease in water level the opposite occurs.

Means for-supplying operating fluid to the diaphragm chamber i8 of the feed control valve I! may comprise a control couple consisting of a flapper 65 and a nozzle 66, the latter being in fluid communication with the valve diaphragm chamber I 8 by means of a pipe 61 which is supplied with fluid under pressure, such as air, through a supply line 66 from a source not shown. The supply line 68 may have a restricted oriflce 69 having a capacity which is less than that of the nozzle 66 so that the pressure in pipe 61 and on diaphragm I 9 is dependent on the degree of nozzle opening aflorded by the flapper 63.

flapper is pivotally secured at 60 to one end of a lever 14 which is, in turn, supported on the free ends of Bourdon tubes I! and 16 by means of pivotal connections 11 and 18 respectively.

The Bourdon tubes may be secured to the usual instrument assembly plate, not shown, by means of base blocks I9 and 66, and through the latter block Bourdon tube 15 may be in communication with the fluid pressure in the nozzle line 61 by means of a pipe 6|.

The controller parts just described are so arranged that en an increase of water level in the steam drum l3 and a consequent counter-clockwise movement of the arm H the flapper 66 is moved toward the nomle 66 around the lever pivot 60 to increase the nozzle pressure and reduce the opening of valve I1 by an amount depending on the increase in water level. At the same time, the increase in nozzle pressure is communicated through pipe 6| to Bourdon tube 15 and the pivotal connection 11 is lowered by an amount depending on the extent of pressure change. The lever 14 is thus turned in a coun- Means for regulating the control setting of the instrument, shown more clearly in Fig. 2, may

include a vernier adjustment member having a shaft 86 swivelly mounted in the end 81 of Bourdon tube I6 and threaded into a support arm 88 for the pivot I8. By raising or lowering the pivot 18, the flapper and nozzle may be placed in controlling relation at any desired boiler water level.

Means for varying the throttling range of the instrument, as required for a particular operating condition, may comprise a vernier adjustment member 90 in operative connection with a ratchet wheel 9I associated with the nozzle 66, and cooperating with ratchet teeth 92 on a guide 93 which is in turn mounted on a base bracket 94. To facilitate movement of the nozzle, the pipe 61 may be provided with a flexible portion 95, the parts being so arranged that the throttling range may be increased or decreased by moving the nozzle toward the lever pivot 60 or in the opposite direction respectively.

The control elements herein described may function to vary the opening of the feed valve I! to maintain the waterlevel in the steam drum I3 over a relatively wide range of level change, or over small increments of level change as may be desired. However, when the water level shrinks or swells, because of an increase or decrease of steam pressure in drum I3, the false level thus created is not a true indication of the actual amount of water in the boiler, or of the change in rate of water consumption. The mechanism, therefore, causes the feed valve II to increase the feed when it should be reduced and vice versa. Thus, a substantial time lag is created which interferes with the operating eiliciency of the boiler and which may cause the water level to vary beyond the limits of safety.

To overcome this difiiculty, I introduce an additional element in the form of the Bourdon tube I0. referred to above. which may be readily incorporated into the instrument assembly at no substantial additional expense. This tube, which is pivoted to the lever I4 at a point between its ends as hereinabove described, serves as a fixed point around which Bourdon tube I5 functions as long as a false water level is not created in steam drum I3 by a sudden change in steam pressure in the drum. However, when a false water level is created, this tube functions to reset the control point of the instrument to maintain or vary the boiler feed during the period of shrinking or swelling as may be required for given operating conditions. To accomplish this, I preferably make Bourdon tube I6 responsive to the pressure of the water on top of the mercury 48 in pct 46 by means of a pipe 96. As long as a true water level is reflected in the drum I3 the mercury 48 rises and falls in response to changes in such level, and compensating tube I5 functions around the Bourdon tube pivot I8 to vary the feed valve opening and control the water level I5 around the set point. When a false level is created by a temporary change in pressure because of a sudden change in load demand, the tube I6 responds, to automatically reset the instrument control point. If, for example, a decrease in vapor pressure occurs causing a false high water level, Bourdon tube I6 raises lever I4 about pivotal'point I1 and lifts the pivoted end of flapper 65 around its support member ID thereby resetting the instrument control point to a higher boiler water level. If it is assumed that the false level is three inches higher than the true level, the parts may be adjusted so that the control point is reset for a level which is three inches higher than the original setting. Thus, the level setting is automatically increased and the flow of water to the boiler is maintained. As the vapor pressure returns to normal and the false level recedes to the true level, the instrument control returns to the normal level setting. On an increase in vapor pressure and a corresponding false low water level, the opposite occurs.

Inasmuch as the extent of false water level change is dependent on the type of installation and on the operating conditions, I provide means. more clearly shown in Fig. 3, for varying the amount of reset and thereby the rate of flow of feed water for any given false change in level. Such means may comprise a Bourdon coil clamp I00 which is secured to the base block I9 substantially at the center of radius of the tube 16 by means of a set screw IN. The free end I02 of the clamp is disposed at an angle and, together with an angle shaped member I03 spaced therefrom and secured to the clamp, as by rivets I04, constitute a pair of jaws which are adapted to make a sliding fit with the flat sides of the tube I6. That portion of the Bourdon tube between the jaws and the fixed end I9 of the tube is thus prevented from responding to changes in vapor reset for a given change in vapor pressure and the false level thereby created may be varied to suit the installation. It may be desirable to reset the level control point by an amount equal to the false change in level, or by an amount less or greater than such change, depending on the type of boiler, the degree of accuracy to which the vapor pressure is controlled, and the operating conditions. The device herein disclosed may be adapted to any set of conditions and will function as soon as a false water level is created to anticipate a subsequent change in true level in the opposite direction and thus may be made to function to maintain the true water level substantially within the normal range of level variation to which the controller is ad- J'usted.

It will be understood that the mercury pots 45 and 46 and associated parts, including the control point reset tube I6 and, if desired, its connecting pipe 96, herein shown included in dotted-line I05, may be assembled in one unit and installed in a standard manometer instrument case ready for connection with the boiler. Thus a compact controller may be provided which is capable of taking care of the conditions enumerated at practically the same cost as a standard manometer. It will be further understood that other level responsive means, such as a thermostatic controller, or a float operated device, may be provided with means for varying the level setting having the characteristics herein described without departing from the spirit or scope of my invention.

I claim:'

1. In a level control mechanism for vapor generators, the combination with means for varying the supply of liquid feed to said generator, of a controller for governing said means, comprising a system in operative connection with said means having a source of fluid under pressure. an exhaust nozzle for said system, a flapper in operative relation with said exhaust nozzle for governing the pressure in said system, and Joint means consisting of an element responsive to varlation'sffiniliquid level in said generator for varying the relative position of said flapper and nozzle to maintain a predetermined normal liquid level in said generator, and an element responsive to a change in pressure in said generator for varying the relative position of said flapper and nozzle tovary the liquid level from said predetermined normal during the period of said pressure change.

2. In a liquid level responsive device for controlling fluid pressure operated means for governing the supply of liquid to a vapor'generator, a fluid pressure system for said means, a source of fluid pressure for said system, a control couple comprising a flapper and nozzle one of which is movable in relation to the other for governing the pressure of fluid in said system, a pair of mercury pots in fluid communication and partially filled with mercury, one of said pots being in fluid communication with said generator at a point below the level of liquid therein and the other of said pots being in fluid communication with said generator at a point above the liquid level, a float in one of said pots in operative connection with a member of said control couple to vary the relative position of said members on a change in liquid level in said generator to provide a predetermined normal liquid level therein, and an element responsive to a change in pressure in said generator in operative connection with a member of said control couple to independently vary the relative position of said members to change the liquid level in said generator from said predetermined normal level during the period of said pressure change.

3. In a liquid level. controller for governing the rate of liquid input to a vapor generator to maintain a predetermined level therein, the combination with a first and a second container in fluid communication with each other and partially filled with a measuring liquid having a specific gravity greater than that of the generator liquid and nonmiscible therewith, said first container being in fluid communication with the generator liquid and said second container with the generator vapor, of an element responsive to variations in level of said measuring liquid, a second element in fluid communication with said second container and responsive to variations in fluid pressure above the surface of measuring liquid therein, liquid supply means for said generator, a valve for governing said means, a

pressure system having a source of pressure for operating said valve, 9. second valve for gover'riing the pressure in said system, and joint means operated by said elements for varying the opening of said second valve. I

4. In a liquid level responsive device, the combination with a fluid pressure system having a source of supply for governing the rate of flow of liquid to a pressure generator, of a valve for governing the pressure in said system, and joint means for varying the opening of said valve including, an element responsive to a change in liquid level in said generator, an element responsive to a change in vapor pressure at the surface of said liquid and means responsive to a change of pressure in said system for modifying the variation in valve opening eflfected by either of said elements.

5. In a level control mechanism for vapor generators, the combination with means for varying the supply of liquid to said generator. of a controller for governing said means, comprising a system in operative connection with.

said means having a source of fluid under pressure, a valve for governing the pressure in said system, and joint means including a movable member for varying the opening of said valve, an element responsive to changes in level oi'gen erator liquid in operative connection with said movable member, and an element responsive solely to changes in generator static pressure in operative connection with said movable member, said first-mentioned element varying the opening of said valve to maintain a predetermined normal level of liquid in said generator, and said last-mentioned element varying the opening of said valve to raise said level on a drop in generator pressure and to lower said level on a rise in generator pressure.

6. In a level control mechanism for a vapor generator, the combination with feed mechanism for varying the supply of liquid to said generator, of a controller for governing said feed mechanism, comprising, a system in operative connection with said mechanism having a source of fluid under pressure, a valve for governing the pressure in said system,,a movable member for operating said valve, and a plurality of means for actuating said movable member, one of said means being responsive to a change of liquid level in said'generat'or for varying the pressure in said system to maintain a predetermined normal level of generator liquid, another of said means being responsive solely to a change of static pressure in said generator for varying the pressure in said system'to raise said level on a drop in static pressure and to lower said level on a rise in static pressure, and another of said means being responsive to a change of pressure in said system for actuating said member to modify the change of pressure in said system initiated by either of said aforementioned means.

7. In combination, a vapor generator, pressure operated means for supplying liquid to be vaporized, a controller in operative connection with said means including a system having a source of fluid under pressure, an exhaust nozzle for the system, a flapper movable in relation to the nozzle to vary the pressure in the system, a plurality of fulcrums for the flapper, a device sensitive to variations in the level of liquid in the generator for changing the position of one of the fulcrums, and means sensitive to changes in static pressure in the generator for changing the position of another of the fulcrums.

8. In combination, a vapor generator, pressure operated means for supplying liquid to be vaporized, a controller in operative connection with said means including a system having a source of fluid under pressure, an exhaust nozzle for the system, a flapper movable in relation to the nozzle to vary the pressure in the system, a fulcrum for the flapper, a device sensitive to variations in the level of liquid in the generator for moving the flapper about the fulcrum,-and means responsive to variations of static pressure in the generator for changing the position of the fulcrum.

HENRY C. EARLE, JR.

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